1. Field of the Invention
The field of the present invention is telescopes, and in particular Gregorian telescopes.
2. Background
Gregorian telescopes are often used for applications in which an upright image is needed. Gregorian telescopes have the additional advantage of not creating strong optical aberrations in images. However, the length needed for the optics of Gregorian telescopes may make such designs difficult or impossible to use in certain applications.
A Gregorian telescope has a primary mirror and a secondary mirror, with the distance between the primary and secondary mirrors being greater than the focal length of the primary mirror. Thus, a Gregorian telescope is necessarily long compared to other telescope designs, such as a Cassegrain telescope, which can have overall lengths that are much less than the focal length of the primary mirror. Other more compact telescope designs, however, may give inverted images and may be more difficult to manufacture if a convex mirror is part of the design. As is generally known by those skilled in the art, it is more difficult to test the optical quality of convex mirrors, such as those used in a Cassegrain telescope, than it is to test the optical quality of concave mirrors. Therefore, for certain applications, Gregorian telescopes have desirable advantages over other telescope designs.
The present invention is directed to a compact telescope of a modified Gregorian design. The modifications to the traditional Gregorian telescope reduce the overall length of the telescope while still maintaining certain benefits of the Gregorian design (e.g., upright image, minor to moderate optical aberrations, and concave mirrors). The compact telescope comprises three optically coupled reflecting surfaces. The first reflecting surface is concave and defined by an outer perimeter and an inner perimeter. The curvature of the first reflecting surface defines a focal plane of the first reflecting surface. The second reflecting surface is optically coupled to the first reflecting surface and disposed between the first reflecting surface and the focal plane. The third reflecting surface is optically coupled to the first reflecting surface by the second reflecting surface and disposed within the inner perimeter of the first reflecting surface. The third reflecting surface is concave and has a curvature that is greater than the curvature of the first reflecting surface. An aperture is included in the third reflecting surface.
In a first separate aspect of the present invention, the first reflecting surface is annular and the second and third reflecting surfaces are radially defined. The second and third reflecting surfaces have equal diameters that are preferably approximately one-third the outer diameter of the first reflecting surface. The size and shape of these reflecting surfaces maximize the viewable light reflected within the telescope while minimizing the central obscuration caused by the second reflecting surface and/or the third reflecting surface.
In a second separate aspect of the present invention, the first and third surfaces form an integral unit. This integral unit includes an annular outer portion and a radially defined inner portion, with the inner portion having a greater concave curvature than the outer portion. The outer portion functions as the first reflecting surface and the inner portion functions as the third reflecting surface. By forming the first and third surfaces as an integral unit, manufacturing techniques may be employed that help reduce optical aberrations due to imprecise alignment of the reflective surfaces.
In a third separate aspect of the present invention, the second reflecting surface may comprise a steering mirror. The steering mirror may be planar or curved. By including a steering mirror with a large radius of curvature, the optical performance of the compact telescope may be improved.
In a fourth separate aspect of the present invention, any of the foregoing aspects may be employed in combination.
Accordingly, it is an object of the present invention to provide a compact telescope based on modifications to the traditional Gregorian design. Other objects and advantages will appear hereinafter.